Currently, internationally advanced gasoline quality standards are divided into four standard systems, namely, United States, European Union, Japan and World Fuel Specification. Although concrete limit values among various gasoline standards are different, the general trend is more and more stringent. European Union enforced ultra-low sulfur (ie 10 ppm) Euro V standards in 2009, Japan enforced ultra-low sulfur standards in 2008, the sulfur content in gasoline standards of U.S. California has been as low as 15 ppm, obviously, low-sulfur gasoline product is a general trend.
Meanwhile, crude oil has lower and lower quality as well as heavier and heavier weight. United States World Refining predicted that world crude oil average API will be declined from 32.5 in 2000 to 32.4 in 2010 and 32.3 in 2015. The sulfur content will be increased from 1.14% in 2000 to 1.19% in 2010 and 1.25% in 2015.
At present, catalytic cracking equipment suitable for deep processing of heavy oil among oil refining devices accounts for more and more proportion in China. The catalytic cracking processing capacity accounts for 33.5% of crude oil processing capacity in China, while the processing capacity of catalytic reforming only accounts for 5.66% of crude oil processing capacity. Alkylation accounts for 0.52% of crude oil processing capacity, therefore, raw materials in Chinese gasoline pool include catalytic gasoline (accounting for 73.8%) and naphtha.
Existing low-sulfur high-octane-number gasoline is prepared by mixing FCC gasoline and naphtha refined product according to different proportions.
Existing domestic catalytic gasoline (FCC gasoline) and main refining route of naphtha are respectively as follows:
Selective catalytic gasoline is selectively hydrogenated for removing diolefin. The products are cut in cutting column to obtain light gasoline and heavy gasoline fractions. The light gasoline is etherified by etherification unit (sulfur content of 50-100 ppm), heavy gasoline is desulfurized by selectively hydrogenation apparatus (sulfur content of 10 ppm or so). The refined FCC gasoline blending component is obtained after etherification and hydrodesulfurization products are mixed. The sulfur content of FCC gasoline refined products is generally about 20 ppm after blending.
The main refining route of naphtha is as follows: naphtha is divided into light naphtha and heavy naphtha fractions after cutting pretreatment. Refined light naphtha components can be obtained from light naphtha fraction by isomerization. A part of dry gas, liquefied gas, hydrogen gas and heavy naphtha reformate are generated by sending the heavy naphtha component after cutting pretreatment into the continuous reforming apparatus. Light aromatic components and heavy aromatic components are separated by cutting reformate. Refining heavy naphtha component (1) can be obtained from light aromatic component after benzene extraction for blending with gasoline. Heavy aromatic component and refined heavy naphtha component are obtained by sending the heavy aromatic component into the cutting column again (2). The refined naphtha blending component can be obtained by blending the obtained refined light naphtha fraction component, refined heavy naphtha component (1) and refined heavy naphtha component (2).
Gasoline with low sulfur content can not be easily obtained due to higher sulfur content in light gasoline. The oil product obtained from naphtha can be blended with FCC refined gasoline. However, since catalytic gasoline (i.e. FCC gasoline) accounts for 73.8% in current gasoline pool in China, naphtha only occupies a small portion, 50% of naphtha is used as raw materials for producing ethylene and aromatics, the naphtha for producing high-grade clean vehicle gasoline is prominently insufficient.
The current production method of producing high-grade clean vehicle gasoline (ie, low-sulfur high-octane-number gasoline) by the above technique has the following shortcomings: {circle around (1)} high investment; two selective hydrogenation units in FCC gasoline refining and continuous reforming unit in naphtha refining have higher investment. The device scale is limited by raw materials, and the resources are not rationally utilized, for example, reformate is the main raw material for producing polyester. A large number of reformate is used as high-octane-number gasoline blending component, thereby the scarce polyester raw materials become more deficient. {circle around (2)} High energy consumption: two selective hydrogenation units used in FCC gasoline refining have higher energy consumption rate. Meanwhile, the continuous refining device and cutting column in naphtha refining belong to devices with high energy consumption rate; {circle around (3)} clean vehicle gasoline with high standards can be produced in whole set and large scale. {circle around (4)} the clean vehicle gasoline with high standards has lower gasoline quality, and the method only can be used for producing low-grade gasoline products; {circle around (5)} Pollutant emissions are serious.
National V (equivalent to European Union V) standard will be firstly adopted in Beijing in 2012. However, China's crude oil mainly includes catalytic cracking gasoline, while the crude oil has worse and worse quality. Existing technique for producing national V gasoline is characterized by high technical cost, high energy consumption, and incapable continuous mass production. Therefore, the technique of producing high-octane-number low-sulfur gasoline with low investment, low energy consumption and high-grade, consistent with market demand, is urgently demanded for solving problems in the technical field.